The project aims at comparing the functional properties of the human senses of smell and the chemical sensory irritation (i.e., chemesthesis) with regard to the detection of volatile organic compounds (VOCs) singly and in mixtures, VOCs have been implicated in the production of adverse sensory effects- particularly irritation of the nose, eyes, and throat-in indoor( e.g., sick building syndrome) and occupational environments. The sensory response of interest will include: odor, nasal pungency, nasal localization, and eye irritation. Nasal pungency entails sensations like prickling, piquancy, tingling, irritation, burning, freshness, stinging, and the like. Nasal localization, or lateralization, entails the ability to pinpoint which nostril received a chemical stimulus when air is simultaneously delivered to the other nostril. Nasal pungency, nasal localization, and eye irritation rest on activation of the trigeminal nerve. Detection of nasal pungency will be tested in subjects lacking olfaction to avoid odor biases. VOCs will be selected from within and across homologous series where carbon chain length provides a convenient "unit of change" of underlying physiochemical properties. For each individual VOC, we will determine the airborne concentration range that spans the sensory response from chance detection to virtually perfect detection, thus obtaining detectability functions. With this information, we will prepare and test mixtures for which individual detectability of the components will have been measured. We will begin by studying binary mixtures and, then, proceed to ternary, quaternary, and higher order mixtures. Systematic selection of VOCs according to gradual changes in physiochemical and measurements of detectability functions will permit to uncover the physiochemical and sensory determinants of the detection of chemical mixtures, compared to the detection of single components, in olfaction and chemesthesis. Knowledge of these determinants is vital for understanding and preventing adverse sensory reactions from air pollution. In addition, use of an improved chemical-delivery system will provide data directly applicable to environmentally realistic (i.e., whole-body) exposures.